PROJECT SUMMARY A significant challenge for understanding social dysfunctions observed in mental illness is to link high-level theories of social behavior and cognition with the computations performed by brain circuits. Specifically, how does the brain translate social perception into social valuation, and how does such valuation influence social actions? We propose to leverage recent developments in economic theory and cognitive neuroscience to bridge this divide using a computational, model-based approach. In this proposal, we hypothesize that social behavior is underpinned by brain mechanisms that are influenced by the neurotransmitter dopamine, and that these mechanisms can be captured by computational models that integrate internal representations of social experience, and parameters relevant to dopamine tone, to inform social actions. Social valuation thus critically, and quantitatively, depends upon both internal social representations and the neurochemistry of the actor within the social environment. To assess this hypothesis, we pursue two approaches to evaluate dopamine tone: one in which we use an FDA-approved medication, tolcapone, to influence dopamine metabolism, and one in which we perform PET imaging to measure dopamine release and baseline dopamine receptor D2/D3 occupancy. We then apply a model of social valuation to subjects' behavior, and search for neural correlates of this valuation using functional MRI (fMRI). To this end, we bring together a group of experts in (1) the neuroeconomics and modeling of social and non-social decision-making, (2) cognitive neuroscience, (3) the pharmacology of frontostriatal circuits, and (4) neuroimaging. We thus seek to broaden our understanding of the computations and circuits underlying social behavior. Moreover, we believe that a model-based understanding of these behaviors and neural circuits may guide more robust predictions of the effects of pharmacological manipulations on social valuation, and provide quantitative tools to assess the effects of such manipulations in patient populations, with possible therapeutic implications.